Actuation mechanisms are involved in downhole drilling and in general are used to activate or deactivate a component of the downhole tool such as a reamer. Actuation mechanisms are typically implemented by dropping an object, usually a ball, down a bore of a downhole tool string. The ball gets caught by an actuation system causing a rise in pressure. As the pressure rises, the ball is pushed through the actuation mechanism which results in the activation or deactivation of the component. The prior art discloses mechanical actuation of downhole tools.
One such actuation mechanism is disclosed in U.S. Pat. No. 4,893,678 to Stokley, which is herein incorporated by reference for all that it contains. Stokley discloses a downhole tool suitable for multiple setting and unsetting operations in a well bore during a single trip. The downhole tool is suspended in the wellbore from a tubing string, and is activated by dropping a metal ball which plugs the passageway through the tubing string, such that the tubing pressure may thereafter be increased to activate the downhole tool. A sleeve is axially moveable within a control sub from a ball stop position to a ball release position, and has a cylindrical-shaped interior surface with an inside diameter only slightly greater than the ball. Collet fingers carried on the sleeve are radially movable from an inward position to an outward position to stop or release the ball as a function of the axial position of the sleeve. Fluid flow through the tubing string is thus effectively blocked when the sleeve is in the ball stop position because of the close tolerance between thse sleeve and the ball, while the ball is freely released from the sleeve and through the downhole tool when the sleeve is moved to the ball release position.
Another such actuation mechanism is disclosed in U.S. Pat. No. 5,230,390 to Zastresek, which is herein incorporated by reference for all that it contains. In Zastresek, a closure mechanism for preventing fluid access to an inner tube of a core barrel assembly is disclosed in which the closure mechanism is configured to move from an open, or unoccluded, condition to an occluded condition in response to increased fluid flow rates and pressure differentials occurring at the closure mechanism. The closure mechanism is also configured to maintain occlusion of the inner tube under substantially all types of drilling conditions, and particularly those where conventional closure mechanisms may fail, such as in horizontal drilling. The closure mechanism generally includes a conduit structure associated with the inner tube, and having a seat, an occlusion structure, such as a ball, and releasing structure which maintains the occlusion structure in spaced relationship to the seat until increasing pressure differentials result in release of the occlusion structure to register the seat.